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Preoperative Evaluation of External Auditory Canal Atresia on High-Resolution CT

¹ All authors: Department of Radiology, Innsbruck University Hospital, Anichstrasse 35, Innsbruck 6020, Austria.

Received April 14, 2003; accepted after revision September 30, 2003.

 
Presented at the 2002 annual meeting of the Radiological Society of North America, Chicago, IL.

Address correspondence to E. M. Gassner.

Introduction

Top Introduction Surgical Approach and Technique Patient Selection High-Resolution CT Findings References

 
External auditory canal atresia occurs in one of 10,000–20,000 births and is bilateral in approximately one third of patients [1]. Patients with external auditory canal atresia experience conductive hearing loss. Given intact sensorineural hearing, surgical restoration of conductive hearing can be achieved. To obtain satisfactory results and prevent complications, physicians must select proper candidates for surgery. Preoperative high-resolution CT of the temporal bone plays a central role in evaluating surgical candidates and planning the operation. The purpose of this pictorial essay is to present a spectrum of isolated and complex patterns of external auditory canal atresia encountered on high-resolution CT and their implications in surgical planning.

Surgical Approach and Technique

Top Introduction Surgical Approach and Technique Patient Selection High-Resolution CT Findings References

 
Two surgical techniques have been established, the transmastoid and the anterior approaches. Both techniques are initiated with a postauricular incision and elevation of the auricle. After the transmastoid approach has been performed, the mastoid air cells are first removed, providing middle ear visualization during the subsequent dissection of the atretic plate [2]. The drawback of this approach is a large mastoid defect, causing an increased risk of local infection problems [2]. For the anterior approach, opening the mastoid cells is avoided by creating a cylindric canal through the atretic plate. Drilling is started posterior to the glenoid fossa and anterior to the mastoid cells and is continued in the direction of the middle cranial fossa to reach the epitympanum below the tegmen to avoid ossicle or facial nerve injury [1, 2]. Both transmastoid and anterior approaches are followed by mobilization of the ossicles attached to the atretic bone (usually the hammer neck). The temporalis fascia is grafted as a new tympanic membrane to the ossicles or to a stapes prosthesis. The newly generated canal is then covered with a skin graft [1, 2].

Patient Selection

Top Introduction Surgical Approach and Technique Patient Selection High-Resolution CT Findings References

 
Although sensorineural hearing is usually maintained in patients without a major congenital syndrome, audiometric evaluation is indispensable to ensure that sufficient sensorineural hearing is present. Unlike unilateral atresia, in which normal speech development is ensured, bilateral atresia requires early amplification with a bone conduction hearing aid and surgery on the more suitable ear in childhood.

Yeakley and Jahrsdoerfer [3] described a 10-point rating scale for the selection of surgical candidates by comparing high-resolution CT findings to postsurgical hearing results. Using nine reproducible criteria, one calculates a score to predict postoperative improvement of the speech reception threshold. The criteria include assessment of the stapes, oval window and round window, middle ear space, mastoid pneumatization, facial nerve course, malleus–incus complex, and incus–stapes connection. One point is given for each item with correct or only slightly dysplastic appearance, with the exception of the stapes, which receives 2 points when presented. The final item consists in the clinical aspect of the external ear, which is added to the CT criteria. A point is assigned for a fairly developed auricle. Patients with more than 5 points on the grading system are considered candidates for surgical reconstruction.

High-Resolution CT Findings

Top Introduction Surgical Approach and Technique Patient Selection High-Resolution CT Findings References

 
Isolated External Auditory Canal Atresia
Atresia consists of an osseous plate with a varying degree of pneumatization superposed laterally to the tympanic cavity (Figs. 1 and 2). Accompanying middle ear dysplasias in patients without a further malformation syndrome are frequently of minor type and follow a typical pattern.

View larger version (114K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1. —2-year-old boy with unilateral external auditory canal atresia on right side. Coronal high-resolution CT scan shows well-pneumatized atretic plate (large arrow) with aerated cells superposed laterally to tympanic cavity. Middle cranial fossa shows normal level (arrowhead), allowing enough space for drilling path. Note intact incudomallear joint (small arrow).

View larger version (125K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2. —7-year-old boy with isolated external auditory canal atresia on right side. Axial high-resolution CT scan shows pneumatized atresia plate and well-aerated tympanic cavity. Ossicle chain is preserved. Note incudomallear (arrowhead) and incudostapedial (arrow) joints revented by horizontal axis rotation of long incus process. Note also auricular malformation.

Incudomallear complex.—The incudomallear joint is usually normal (Figs. 1, 2, and 3A) with a rudimentary hammer handle attached to the atretic plate (Figs. 3A and 3B). Severe incudomallear dysplasia (Figs. 3C and 3D) is rare. A dysplastic incudomallear complex has to be resected and the stapes is grafted to the temporalis fascia.

View larger version (132K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3A. —6-year-old boy with bilateral external auditory canal atresia and no other congenital malformations. Coronal high-resolution CT scan obtained through right tympanic cavity shows hammer-handle rudiment attached to pneumatized atresia plate (arrow). Incudomallear joint (arrowhead) has normal aspect. Tympanic cavity shows normal width. Cochlea shows normal development. Note auricle dysplasia.

View larger version (128K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3B. —6-year-old boy with bilateral external auditory canal atresia and no other congenital malformations. Axial high-resolution CT scan shows well-pneumatized atresia plate with attachment of hammer-handle rudiment (arrowhead). Good aeration of atresia plate and sufficient tympanic cavity width provide enough space for drilling. Patient shows lateral displacement of descending facial nerve segment (arrow) passing along atresia plate. Care must be taken to pass anteriorly to descending facial nerve segment when drilling through atretic plate.

View larger version (119K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3C. —6-year-old boy with bilateral external auditory canal atresia and no other congenital malformations. Axial high-resolution CT scan obtained through left tympanic cavity shows ossicle dysplasia with fused incus–malleus complex (large arrow) but normal stapes (small arrow). Correctly present stapes could be anchored to fascia graft. However, malformed incus–malleus complex would make contralateral ear preferable for reconstruction. Well-pneumatized atresia plate with lateral displacement of descending facial nerve segment (arrowhead) can be recognized similar to right side.

View larger version (134K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3D. —6-year-old boy with bilateral external auditory canal atresia and no other congenital malformations. Coronal high-resolution CT scan obtained through left tympanic cavity shows malformed incus–malleus complex (arrowhead).

Incudostapedial connection.—Integrity of the incudostapedial joint is best evaluated in the coronal planes (Figs. 3E and 4). Horizontal axis rotation of the long incus process with an obtuse angle to the lenticular process (Fig. 3E) may be seen, with both the incudomallear and the incudostapedial joint recognizable on the same axial slice (Fig. 2).

View larger version (133K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3E. —6-year-old boy with bilateral external auditory canal atresia and no other congenital malformations. Coronal high-resolution CT scan at right incudostapedial joint level shows horizontal axis rotation of long incus process (large arrow) with angle obtuse to stapes (small arrow). Ossicle chain integrity can be shown with high-resolution CT, so that ossicles can possibly be maintained in reconstruction. Mastoid facial nerve canal is displaced to anterior with stylomastoid foramen (arrowhead) opening in anterolateral direction.

View larger version (122K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4. —5-year-old boy with unilateral external auditory canal atresia on right side. Coronal high-resolution CT scan obtained through mesotympanum shows normal incudostapedial joint. Large arrow indicates articulation between lenticular process of incus and stapes head. Small arrow shows normally shaped long incus process. Note well-pneumatized atresia plate providing enough space for drilling to reach epitympanic recess and further on to enlarge newly drilled canal in caudal direction.

Oval window and round window.—Patients with an atretic oval window are not considered candidates for surgical repair [2]. The vertical oval window diameter should measure at least 1 mm [3]. A patent round window is essential for membranous wave transmission of the cochlea. Patients without a congenital syndrome usually show open windows, even with considerable middle ear dysplasia (Fig. 5A).

View larger version (119K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5A. —7-year-old boy with unilateral left-sided external auditory canal atresia. Coronal high-resolution CT scan obtained through middle ear shows oval window (black arrow) and round window (black arrowhead) with normal diameters. Large white arrow points to inferiorly displaced tympanic facial nerve segment overlying oval window. Slight caudal rotation of posterior stapes crus (small white arrow) due to close relationship between facial nerve and stapes can be seen. Middle ear space space is reduced. Stylomastoid foramen (white arrowhead) is displaced in anterolateral direction. Because patient experiences unilateral atresia, operative reconstruction is not recommended.

Middle ear cavity.—Aerated tympanic cavity with preserved function of the tuba auditiva (Fig. 5B) is indispensable for successful surgery. Reduced middle ear space was correlated with unfavorable outcome of surgery [3]. A tympanic cavity width less than 3 mm from the promontory to the atretic plate in the coronal plane is considered inadequate for reconstruction (Figs. 5A, 6, and 7A).

View larger version (143K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5B. —7-year-old boy with unilateral left-sided external auditory canal atresia. Axial high-resolution CT scan obtained through tympanic cavity shows rather widened osseous segment of eustachian tube (black arrowhead) accompanied by tensor tympani muscle (white arrowhead). Correct development and function of eustachian tube are indispensable for middle ear and mastoid aeration. Arrow points to dislocated course of vertical facial nerve segment, descending within atresia plate.

View larger version (135K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 6. —8-year-old girl with bilateral external auditory canal atresia and severe auricle and middle ear dysplasia. Clinical and genetic examinations did not reveal any hints of congenital syndrome. Coronal high-resolution CT scan obtained through oval window shows reduced middle ear space. Epitympanum contains malleus and incus rudiments (large white arrow). Small white arrow indicates posterior stapes crus. Note low middle cranial fossa due to nonaerated temporal bone. Descending facial nerve is displaced in anterior direction crossing tympanic cavity (arrowheads), leading to unpredictable risk for nerve injury during surgery. Mastoid facial nerve canal is shortened with anterolateral rotation of stylomastoid foramen (black arrow). In extreme lateral dislocation of stylomastoid foramen, extracranial facial nerve segment can cause lesions during elevation of auricle.

View larger version (129K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 7A. —17-year-old girl with bilateral external auditory canal atresia. Patient underwent surgery on left side 1 yr earlier, at age 16. Coronal high-resolution CT scan through right tympanic cavity shows contact of long incus process to atresia plate (arrow) in slightly reduced middle ear space. Mobilizing incus from atretic plate may risk ossicle chain injury and labyrinthine trauma transmitted through stapes.

Temporal bone pneumatization.—Aeration of the mastoid cells frequently correlates to pneumatization of the atretic plate (Figs. 2 and 3B). Poor pneumatization of the temporal bone results in reduced space for surgical approach. The temporomandibular joint is displaced posteriorly with close relationship to the tympanic cavity (Fig. 7B). The middle cranial fossa shows a deep position (Fig. 6) in reduced or absent temporal bone aeration. The postoperative coronal plane view provides the steep drilling pathway to avoid opening the middle cranial fossa (Fig. 7C).

View larger version (130K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 7B. —17-year-old girl with bilateral external auditory canal atresia. Patient underwent surgery on left side 1 yr earlier, at age 16. Axial high-resolution CT scan through right tympanic cavity shows thick, poorly pneumatized atresia plate; markedly reduced mastoid ventilation; and decreased size of middle ear. Image also reveals high position of temporomandibular joint (large arrow) with close relationship to tympanic cavity. Poor temporal bone pneumatization leaves little space for drilling between temporomandibular joint anteriorly and descending facial nerve segment posteriorly. Patient has normal stapes (small arrow) with easily depicted crura. Correct cochlea segmentation (arrowhead) is present.

View larger version (126K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 7C. —17-year-old girl with bilateral external auditory canal atresia. Patient underwent surgery on left side 1 year earlier, at age 16. Postoperative coronal high-resolution CT scan shows granulation tissue restenosis. Stapes anchored to facia graft is indicated by arrow. Note close relationship of drilling canal to tympanic and descending facial nerve segments (arrowheads). Image shows low level of middle cranial fossa, forcing surgeon to select steep drilling path in mediocranial direction to reach epitympanum without causing lesions of middle cranial fossa.

Stapes.—Stapes has a significant impact on surgery planning. Although the intact stapes can be anchored to the fascia graft (Figs. 7C and 7D), the dysplastic or absent stapes has to be replaced with a prosthesis [3] with a less predictable outcome [1].

View larger version (137K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 7D. —17-year-old girl with bilateral external auditory canal atresia. Patient underwent surgery on left side 1 year earlier, at age 16. Postoperative axial high-resolution CT scan of left temporal bone shows restenosis due to granulation tissue after external auditory canal reconstruction. Stapes anchored to fascia graft is indicated by arrowhead. Drilling canal passes close to second facial nerve genu (arrow).

Facial nerve.—The course of the facial nerve is often altered and is one of the most important aspects to be considered when planning the surgical approach [1–3]. Unfavorable or undefined nerve course precludes surgical repair [3]. The descending segment is frequently displaced in the ventral and lateral directions with the facial nerve passing along or through the atretic plate (Figs. 3B, 3C, and 5B). Anterolateral displacement of the stylomastoid foramen (Figs. 5A and 6) may lead to extracranial facial nerve injury during elevation of the auricle [1]. In its tympanic segment, the facial nerve may be displaced caudally, overlying the oval window (Figs. 5A and 8A). Typically, the pyramidal eminence with the second genu is displaced anteriorly in the tympanic cavity (Fig. 8B).

View larger version (132K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 8A. —13-year-old boy with unilateral external auditory canal atresia on right side. Coronal high-resolution CT scan shows tympanic facial nerve segment (arrow) and relationship to oval window (arrowhead). Caudal displacement can be seen with nerve obscuring oval window. Tympanic facial nerve segment overhanging oval window puts nerve at risk during surgery.

View larger version (128K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 8B. —13-year-old boy with unilateral external auditory canal atresia on right side. Axial high-resolution CT scan shows anterolateral displacement of pyramidal eminence (site of second facial nerve genu, arrow) moved into tympanic cavity and leading to deep sinus tympani (large arrowhead). Small arrowhead indicates stapes.

External Auditory Canal Atresia in Congenital Malformation Syndromes
Contrary to patients with isolated external auditory canal atresia, patients with an underlying congenital syndrome show a higher degree of external and middle ear deformity [4] and achieve low scores on the Yeakley-Jahrsdoerfer grading system [3]. Inner ear pathologic changes can occur in certain syndromes.

Goldenhar's syndrome.—Goldenhar's syndrome is part of the craniofacial anomaly spectrum with malformation of the first and second branchial arch derivatives, characterized by facial and temporal bone hypoplasia but also involving ectodermal structures such as the otic placode [5]. Severe dysplasia occurred in the external and middle ear of the patient in Figure 9A, 9B, 9C. The middle ear cavity was not aerated (Fig. 9A) because of obliteration of the eustachian tube (Fig. 9B). No ossicle structure is visible (Fig. 9A). Mastoid pneumatization was absent, causing a deep middle cranial fossa (Fig. 9C). The most important finding, however, is an atretic oval window (Figs. 9A and 9C). A closed oval window and obliteration of the eustachian tube exclude surgical repair.

View larger version (124K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 9A. —7-year-old boy with Goldenhar`s syndrome presenting with hemifacial microsomia and temporal bone dysplasia on left side. Axial high-resolution CT scan through tympanic cavity shows nonaerated middle ear cavity (black arrow) due to obliteration of eustachian tube. Ossicles are not present, and oval window is closed by osseous plate (arrowhead). Mastoid cells are not developed. Inner ear presents with normal appearance of cochlea and modiolus (small white arrow). Patient has aberrant facial nerve course with vertical segment descending from geniculate ganglion along anterior pyramidal petrous ridge (large white arrow).

View larger version (132K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 9B. —7-year-old boy with Goldenhar`s syndrome presenting with hemifacial microsomia and temporal bone dysplasia on left side. Axial high-resolution CT scan at skull base level reveals obliterated eustachian tube (arrows) stretching along carotid canal (A). Image also shows agenesis of auricle.

View larger version (125K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 9C. —7-year-old boy with Goldenhar`s syndrome presenting with hemifacial microsomia and temporal bone dysplasia on left side. Coronal high-resolution CT scan at internal auditory canal level shows patent round window (arrowhead) but atretic oval window (arrow), making surgical repair impossible. Image also reveals low middle cranial fossa.

Treacher Collins syndrome.—Similar to Goldenhar's syndrome, Treacher Collins syndrome is part of the craniofacial dysplasia complex caused by a malformation of the first and second branchial arch derivatives, but represents an inherited disorder with bilateral midface hypoplasia, micrognathia (Fig. 10A), and external and middle ear deformity [6]. Surgical exclusion criteria here include small, nonaerated middle ear rudiments, unrecognizable windows, undefined facial nerve course, and a deep middle cranial fossa (Figs. 10B, 10C, 10D, 10E).

View larger version (142K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 10A. —1-year-old boy with genetically proven Treacher Collins syndrome. Volume-rendered CT scan of skull shows bilateral midface hypoplasia with short maxilla, absent zygoma, and hypoplastic mandible. External auditory canal atresia can be recognized.

View larger version (102K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 10B. —1-year-old boy with genetically proven Treacher Collins syndrome. Axial high-resolution CT scan reveals severely hypoplastic nonaerated tympanic cavity (large white arrow) on right side containing small ossicle rudiments. Labyrinthine changes are present with globular deformity of vestibule and lateral semicircular canal (small white arrow). Healthy cochlear segmentation and modiolus (arrowhead) are shown on left side. Internal auditory canal (black arrows) follows ventral direction. Note dysplasia of right and absence of left auricle.

View larger version (91K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 10C. —1-year-old boy with genetically proven Treacher Collins syndrome. Coronal multiplanar reformatted CT scan shows nonaerated hypoplastic middle ear cavity on right side (arrow) with caudal opening to infratemporal soft tissue. Dys-plastic ossicle masses can be recognized in tympanic cavity. On left side, only small soft-tissue–filled tympanic cavity rudiment (arrowhead) is present. Note deep middle cranial fossa due to nonaerated temporal bone.

View larger version (96K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 10D. —1-year-old boy with genetically proven Treacher Collins syndrome. Coronal multiplanar reformatted CT scan shows labyrinthine deformity with globular lateral semicircular canal (arrows) on both sides.

Pierre Robin sequence.—The Pierre Robin sequence comprises the bilateral cleft palate, retrognathia (Fig. 11A), and glossoptosis [7]. To our knowledge, middle and inner ear deformities have not yet been described. Figure 11A, 11B, 11C presents a patient with evidence of a Pierre Robin sequence and external auditory canal atresia. Despite having normal ossicles and patent windows, our patient had a dehiscent facial nerve in the middle ear cavity and reduced tympanal width (Fig. 11B). The dehiscent facial nerve represents an unpredictable risk for surgical reconstruction. Our patient showed an unusual labyrinthine malformation with absent posterior semicircular canal (Fig. 11C) as a possible hint for further membranous labyrinthine deficiency.

View larger version (167K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 11A. —3-year-old boy with clinical features of Pierre Robin syndrome presenting with bilateral cleft, micrognathia, and glossoptosis. Volume-rendered CT scan of skull shows bilateral cleft with premaxilla, mandible hypoplasia, and partial zygomatic defect. Frontal cranioplasty was performed because of premature coronal synostosis. Atresia of external auditory canal was present on both sides.

View larger version (132K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 11B. —3-year-old boy with clinical features of Pierre Robin syndrome presenting with bilateral cleft, micrognathia, and glossoptosis. Axial high-resolution CT scan obtained at oval window level reveals reduced epitympanic space with adherent short incus process (large arrowhead), but correctly developed incudomallear joint (large arrow). Small arrow indicates normally shaped stapes with patent oval window. Dehiscent facial nerve, representing unpredictable risk in case of surgical reconstruction, is shown by small arrowhead.

View larger version (127K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 11C. —3-year-old boy with clinical features of Pierre Robin syndrome presenting with bilateral cleft, micrognathia, and glossoptosis. Axial high-resolution CT scan obtained through labyrinth shows healthy vestibule and horizontal semicircular canal. Posterior semicircular canal crura (arrows), usually seen next to posterior petrous bone ridge, are absent.

References

Top Introduction Surgical Approach and Technique Patient Selection High-Resolution CT Findings References

 

1. Lambert PR, Dodson EE. Congenital malformations of the external auditory canal. Otolaryngol Clin North Am1996; 29:741 –760[Medline]
2. Molony TB, de la Cruz A. Surgical approaches to congenital atresia of the external auditory canal. Otolaryngol Head Neck Surg 1990;103:991 –1001[Medline]
3. Yeakley JW, Jahrsdoerfer RA. CT evaluation of congenital aural atresia: what the radiologist and the surgeon need to know. J Comput Assist Tomogr 1996;5:724 –731
4. Mafee MF, Valvassori GE. Radiology of the craniofacial anomalies. Otolaryngol Clin North Am1981; 14:939 –988[Medline]
5. Lam CH. A theory on the embryogenesis of oculo-auriculo-vertebral (Goldenhar) syndrome. J Craniofac Surg2000; 11:547 –552[Medline]
6. Marszalek B, Wojcicki P, Kobus K, Trzeciak WH. Clinical features, treatment and genetic background of Treacher Collins Syndrome. J Appl Genet 2002;43:223 –233[Medline]
7. Holder-Espinasse M, Abadie V, Cormier-Daire V, et al. Pierre Robin sequence: a series of 117 consecutive cases. J Pediatr2001; 139:588 –590[Medline]

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This Article Figures Only Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Gassner, E. M. Articles by Jaschke, W. R. Search for Related Content PubMed PubMed Citation Articles by Gassner, E. M. Articles by Jaschke, W. R. Social Bookmarking                      What's this? Hotlight (NEW!) What's Hotlight?